The present invention relates to a composition intended to be placed in a well drilled in the ground in order to release tubes or drillpipes stuck by a differential pressure effect or mechanically. The present composition is particularly well-suited for water-base drilling fluids.
It is well-known in the art of oil drilling, or others, that there is in many cases a risk of sticking of the drill stem during operation or of the casing pipes as they are set in the well. The causes can have a mechanical origin or be due to the differential pressure prevailing between the inside of the well and the pores of the rock. In fact, the density of the drilling fluid that fills the well is generally such that the hydrostatic pressure created is higher than the pressure of the fluids contained in the pores of the rock formation crossed by the wellbore. Most drilling fluids contain low-water-loss additives preventing filtration of the drilling fluid in the permeable formation through creation of a cake (deposition on the walls of a layer of colloidal particles) whose impermeability quality conditions the quantity of fluid filtered. Drillpipes that stop rotating can stick to the walls, against or in the cake. The thicker the cake, the greater the sticking surface and the greater the force required for unsticking since it is equal to the value of the differential pressure in relation to each side of the cake multiplied by the contact or adhesion surface. In order to release the drill stem, it is common practice to inject a certain volume of a fluid referred to as spotting fluid at the level of the sticking zone in the form of a volume of some cubic meters of a slug injected into the pipes and set in the sticking zone by circulation of another fluid, generally the drilling fluid. The nature of the spotting fluid must be suited to the circulating setting method, i.e. its density must be equivalent to that of the fluid already in place, its viscosity must be such that injection and circulation in the well pose no problems, and it must meet the discharge quality standards in force. There are many spotting fluid compositions, notably those based on mineral lubricating products.
Document U.S. Pat. No. 4,964,615 describes a spotting fluid based on fatty acid ester, an oleophilic bentonite and an emulsifying system. This fluid does not have the optimized composition of the present invention.
The present invention thus relates to a well fluid for releasing tubular elements stuck in the well. This fluid comprises:
a part A consisting of one or more esters obtained by reaction of a linear or branched monocarboxylic acid (A.1) having between 8 and 24 carbon atoms and a linear or branched polyol (A.2) having between 2 and 20 carbon atoms, the acid: alcohol (A.1:A.2) molar ratio ranging between 1:1 and (n-n/10):1, where n is the number of hydroxyl groups of alcohol A.2,
a part B consisting of one or more linear or branched monocarboxylic acids having between 8 and 24 carbon atoms, the carboxylic acid A.1 and part B being each separately a mixture of at least 80% carboxylic acids having between 1 and 3 insaturations,
a part C consisting of one or more esters obtained by reaction of a linear or branched monocarboxylic acid having between 2 and 24 carbon atoms and a linear or branched monoalcohol having between 2 and 24 carbon atoms, or of one or more linear hydrocarbon chains having at least one insaturation comprising between 8 and 24 carbon atoms, or of one or more branched hydrocarbon chains, saturated or having at least one insaturation comprising between 8 and 24 carbon atoms, said part C having a viscosity lower than about 10 mPaxc2x7s at 40xc2x0 C.,
possibly a part D consisting of a tertiary amine,
and the quantity of part C is determined in relation to the other components in such a way that the viscosity of said fluid is lower than 40 mPaxc2x7s at 40xc2x0 C.
Parts A, B and D can respectively range between the following proportions: between 75 and 90% for A, between 5 and 15% for B, at most 10% of part D, in relation to the total weight of mixture A+B+C.
Parts A, B and D can respectively have the following proportions: 85.4%, 9.5% and 5.1%.
Part A can be pentaerythritol monooleate.
The tertiary amine can be triethanolamine.
The proportion of part C can range between about 60 and 80% in relation to the total weight of the composition.
Part C can mainly consist of 2-ethyl-hexyl oleate.
In this case, a first variant according to the invention can consist in adding at most 40%, in relation to the total weight, of isopropylmyristate.
In the case where part A is mainly pentaerythritol monooleate, a second variant can consist in adding at most 40%, in relation to the total weight, of an ester selected from the group made up of polyglycerol polyricinoleate, polyglycerol monooleate, triheptanoate ethoxylated three times, and mixtures thereof.
In a third variant, it is possible to add at most 40%, in relation to the total weight, of polymerized polyols between dimer and tetramer, linear or branched monoalcohols having between 2 and 10 carbon atoms, or mixtures thereof.
In this third variant, the alcohols can be selected from the group made up of polyglycerol, butanol and a mixture thereof.
In the fluid according to the invention, it is possible to add at most 5% viscosifying agents intended for organic media and a determined quantity of weighting agents.
At most 5%, preferably at most 2% of a wetting and/or dispersing agent can be added.
At most 10% water can also be added.
The present invention also relates to a method for releasing a drill stem stuck in a well, wherein a volume of a fluid as defined above is injected into the well.
The various constituents of the composition according to the invention are non-toxic and non-polluting according to the criteria known in the trade. Of course, considering the different regulations in force according to countries, some products used might be considered acceptable by some countries and not by others as regards the environment.
The spotting fluid can be used as it is in the form of a liquid slug possibly comprising a small proportion of water, or mixed with the water-base drilling fluid, possibly with the oil-base fluids or equivalents.